Radio Access Network (RAN) user plane congestion occurs when the demand for RAN resources exceeds the available RAN capacity to deliver the user data for a period of time. RAN user plane congestion leads, for example, to packet drops or delays, and may or may not result in degraded end-user experience.
In order to cope with RAN user plane congestion, different issues must be addressed. One of them is the application of congestion mitigation measures. Such measures include traffic prioritization, traffic reduction and limitation of traffic. Congestion mitigation measures are implemented to manage user plane traffic across a range of variables including the user's subscription, the type of application, and the type of content.
The Third Generation Partnership Project (3GPP) has discussed several options to cope with user plane congestion (UPCON) and has agreed on the architecture shown in FIG. 1.
A new logical function entity, a RAN Congestion Awareness Function (RCAF) 100, is included in the architecture to report RAN User Plane Congestion Information (RUCI) to a PCRF 102 for the purpose of congestion mitigation. The RCAF 100 is in electrical communication with the Policy Control and Charging Rules Function (PCRF) 102 via an Np reference point. The RACF is also in electrical communication with a RAN Operations, Administration and Maintenance (RAN OAM) module 104 and with a Mobility Management Entity (MME) or Serving General Packet Radio Service Support Node (SGSN) (for the remainder of this specification the MME is referenced as 106a and the SGSN is referenced as 106b) via a Nq or Nq′ reference point.
It is noted that the term “electrical communication” encompasses both wired and wireless electrical communication. Therefore, electrical communication may be, for example, a network communication over a wired connection or a network communication of over a radio frequency connection.
The RCAF 100:                Collects raw user plane congestion information from the RAN OAM 104. The RAN OAM 104 corresponds to Operations Support System (OSS) level features of a RAN operator;        Determines a list of user equipments (UEs) impacted by user plane congestion;        Integrates an RAN congestion status with an integration time fitting with Core Network (CN) mitigation tools (e.g., to provide the PCRF 102 with only information on sustained congestion);        Provides “spatial” integration of RUCI, if the RUCI associated with a cell should depend on a congestion status in neighbouring cells (e.g., in case intra-eNB mobility reporting is not activated).        
The PCRF 102 may then provide policies for congestion mitigation. The introduction of the RCAF 100 involves the addition of the following reference points:                Np: Between the RCAF 100 and the PCRF 102. Over Np, RUCI is sent from the RCAF 100 to the PCRF 102.        Nq/Nq′: Via Nq, the MME 106a provides the RCAF 100 with the list of UEs (e.g., International Mobile Subscriber Identities (IMSIs)) in a given area (e.g. an Enhanced Node B (eNB) ID or an E-UTRAN Cell Global Identifier (ECGI) as disclosed in section 6.1.5.5.2.1 of 3GPP TR 23.705 v0.11.0) and for each of the IMSI(s) the Access Point Names (APNs) of the active Packet Data Network (PDN) 108 connections. The Nq′ reference point is between the RCAF 100 and the SGSN 106b and is used, for a set of IMSI(s), to provide the RCAF 100 with the list of APNs of the active PDN 108 connections of each of these IMSIs.        
Based on the parameters and their values received from the RAN OAM 104, the RCAF 100 reports a congestion level to the CN (e.g., to the PCRF 102). In accordance with the reported congestion level, the operator configures the mitigation policies in the CN.
RUCI is defined over the Np interface and includes the following information:                Congestion/abatement location information (e.g. eNB ID or Cell ID or 3G Service Area ID);        A congestion level;        The validity time of the information—when this time has elapsed and no further congestion information has been received, the congestion is assumed to be over; and        A list of IMSI(s) for the affected UEs.        
The set of congestion mitigation actions that could be executed is not comprehensive, as only actions that are applied on the networks are considered.
Further, the PCRF 102 is not aware of:                The topology of the 3GPP and any alternative access networks—i.e., it does not know whether for a given cell there are alternative access networks for a UE or not; and        Which of the UEs included in the RUCI report for a given cell can actually switch access network.        